The purpose of this study is to investigate the nature of the human T cell response during the course of acute sporadic hepatitis C and during the course of interferon therapy for chronic hepatitis C. Peripheral blood lymphocytes, plasma and serum will be collected from patients with acute non-A, non-B hepatitis or from patients who have enrolled in a trial in interferon-alfa therapy of chronic hepatitis. Studies have also been expanded to include three new assays for anti-HCV.